(1) Field of the Invention
The invention is related to an energy absorbing system that is adapted for absorbing energy of an object in a vehicle in a crash situation by decreasing acceleration and force acting on said object in said crash situation. The invention is further related to a vehicle seat and to a vehicle having a seat provided with such an energy absorbing system.
(2) Description of Related Art
An Energy Absorbing System (EAS), which may also be referred to as an Energy Absorption/Attenuation System, is usually provided in a crashworthy seat of a vehicle, such as an aircraft, for protecting an occupant of the crashworthy seat e.g. in a crash situation of the vehicle by reducing an occurring body load. Currently, complex EAS exist that are automatically electronically adjustable, for instance by using magneto-rheological fluids. Furthermore, fixed-force EAS with multiple different functioning principles exist, which are generally cheaper and easier to manufacture.
The document US2002/0079725 describes an exemplary fixed-force EAS for absorbing energy of a vehicle or component of a vehicle or occupant of the vehicle in a crash situation so as to allow relatively gradual deceleration of the vehicle, component or occupant. This fixed-force EAS includes a first part, a second part and an elongate deformable member secured to the first part and extending through a deforming arrangement carried by the second part. The elongate deformable member normally acts as a tie or strut between the first and second parts, but the arrangement is such that, when the force acting between these first and second parts exceeds a predetermined amount in a predetermined direction, the elongate deformable member is forced progressively through the deforming arrangement as the distance between the first and second parts changes and the deformable member is thereby forced to undergo plastic deformation, whereby energy is absorbed. The deforming arrangement is such as to effect such plastic deformation substantially without changing the material cross sectional area of the deformable member.
More specifically, the fixed-force EAS according to the document US2002/0079725 is implemented as a roller-tube assembly, wherein the deforming arrangement is provided by means of a roller arrangement having rollers with fixed, i.e. predefined, distances relative to each other, and the deformable member is provided by means of a plastically deformable attenuation tube. In other words, energy absorption/attenuation is performed by deformation of the attenuation tube by means of the rollers with the predefined distances relative to each other.
However, by fixing the distances between the rollers of the roller arrangement to such predefined distances, the rollers may only transmit a predetermined compression force to the plastically deformable attenuation tube for plastically deforming the latter. Consequently, this system can only be manually and stepwise adjusted by adding and connecting additional roller-tube assemblies.
The document US2002/0079725 further describes that manual or automatic adjustment of the energy absorbing characteristics of the described roller-tube assembly can be achieved in a number of ways, including:
(1) Adjustment of wall thickness by rotating, about its longitudinal axis, an attenuation tube having a circular cross-section exterior and a non-circular internal cross-section, to various positions within the roller arrangement, so as to vary the force required to flatten or deform the attenuation tube and hence to alter the attenuation characteristics.
(2) Partially pre-deforming, e. g. flattening, the attenuation tube varying amounts:                (2.1) Rotation of an attenuation tube having a noncircular form of constant or varying wall thickness such that different parts of the periphery of the attenuation tube are presented to the rollers of the roller arrangement so that different forces are needed to deform the attenuation tube, thus providing adjustment for different occupants.        (2.2) Varying a predefined gap between the rollers of the roller arrangement or equivalent parts of the respective deforming arrangement, thereby increasing or decreasing the force required to flatten/deform the attenuation tube.        
(3) Varying the roller diameter via tapered cones. In a similar fashion to (2.2) above, the gap that the attenuation tube is required to pass through may be either increased or decreased by moving the rollers of the roller arrangement or other corresponding fixed members as appropriate to present the desired diameter to the attenuation tube, thus, changing the attenuation properties.
However, while the document US2002/0079725 describes that the energy absorbing characteristics of the described roller-tube assembly can be adjusted manually or automatically and further enumerates a number of ways how this can be achieved, it remains silent on concrete realizations. For instance, one described way consists in varying a predefined gap between the rollers of the roller arrangement for increasing or decreasing the force required to flatten/deform the attenuation tube. Nevertheless, it is not described how this variation is performed, whether it is performed manually or automatically, whether it is performed between different discrete predefined gap values and so on.
The document US2009/326765 describes load limiting on a seat belt buckle by providing an adjustable energy absorbing device mounting the seat belt buckle. Vehicle and occupant conditions are electronically sensed to determine the optimal adjustment of the adjustable energy absorbing device. The adjustable energy absorbing device is an extendable strut having an end connected to the buckle and an end connected to the vehicle. The strut has metal deforming elements to be deformed upon the load reaching a certain magnitude by ball shaped plow shoes.
The document US2009/322066 describes a load limiting device for mounting a seat belt buckle that also includes a plow shoe attached to one of the buckle and a pair of opposed plates attached to the other of the buckle and the vehicle. The plow shoe travels between the plates and absorbs energy by deforming at least one of the plates. An electronic adjuster mechanism adjusts the distance between the opposed plates to selectively increase or decrease the energy absorbing capacity of the load limiting device.
The document U.S. Pat. No. 5,273,240 describes an impact energy absorption system for aircraft seats. A seat is movable between a first unloaded position and a second crash induced position. A deforming die and an additional set of die jaws are connected to a seat mounting and defines an aperture of variable size. A deformable rod has a shoulder connecting the seat to the mounting the rod passing through the deforming die and the variable die jaws. During crash induced movement of the seat, the rod is pulled through the deforming die.